Narrow fiberglass knit tape

ABSTRACT

The present invention provides a narrow orthopedic casting tape which can be handled in longer lengths suitable for economical production of coated fabric products. The narrow casting tape of the present invention is knitted as a wide fiberglass fabric with at least one removable connecting yarn in the length (i.e., warp) direction of the fabric which acts to connect two narrower strips of fiberglass fabric. The removable connecting yarn is subsequently removed from the fabric by a heat treatment process which separates the wider fabric into two narrower fabrics and also heat sets the fabric. Alternatively, the removable connecting yarn may be removed from the fabric by a dissolution process. Narrow fabrics of the present invention can also be constructed of organic yarns. 
     The present invention also provides a tearable orthopedic casting tape which has a high degree of extensibility. The tearable casting tape of the present invention is knitted as a wide fabric, preferably fiberglass, with at least one tearable connecting yarn in the length direction of the fabric which acts to weakly connect two or more narrower fabrics. The tearable connecting yarn is capable of being easily torn or slit causing the fabric to separate into narrower webs.

FIELD OF THE INVENTION

This invention relates to the field of knitted fiberglass fabrics. Moreparticularly, it relates to a method of forming narrow knittedfiberglass fabrics. More particularly, it relates to extensible knittedfiberglass fabrics which are coated or impregnated with a liquid resinwhich cures to form rigid reinforced fiberglass articles. Another aspectof the invention relates to a wide knitted fiberglass fabric which maybe easily separated (e.g., torn) into two or more narrower fiberglassfabrics. A preferred embodiment of the invention relates to orthopediccasting tapes comprising resin-coated or impregnated, extensible,knitted fabrics.

BACKGROUND OF THE INVENTION

Plaster of Paris casts have been in use to immobilize body members orlimbs for some time. In recent years, the plaster of Paris bandages havebeen superseded by synthetic casting tapes which employ polymericmaterials on a fiberglass substrate. The polymeric materials are of thetype that cure by exposure to actinic radiation or cure when reactedwith water. More recently, water-cured or water-reactive polyurethanecompositions have been used in forming orthopedic casts and thepolyurethane compositions have largely supplanted other polymericsynthetic casting materials. The polyurethane casting materials are ofthe type which are disclosed in U.S. Pat. Nos. 4,667,661; 4,609,578;4,411,262; and 4,376,438.

High modulus fibers such as fiberglass are commonly used as resinreinforcements in composite materials to impart strength to the curedarticle. In some applications the fiberglass yarn is woven or knit intoa fabric which can then be treated with a finish, resin or othercoating. Compared to organic fibers such as polyester, glass fibersexhibit virtually no elongation and are more prone to breakage duringprocess operations such as knitting and weaving. Because the fiberelongation is essentially nil, glass fabrics do not stretch unless theyare constructed with very loose loops which can deform upon applicationof tension, thereby providing stretching of the fabric. Knitting withloosely formed chain stitches imparts extensibility by virtue of itssystem of interlocking knots and loose loops.

An important usage of knitted fiberglass fabrics is in the manufactureof orthopedic cast bandages where those fabrics are coated orimpregnated with a curable resin and packaged as rolls of casting tape,which are subsequently used by a physician or medical clinician toconstruct orthopedic casts. When constructing an orthopedic cast from aroll of casting tape (typically ˜100 millimeters (mm) wide), it isnecessary to change the direction of wrapping to accommodate bodycontours such as the heel of the foot. This requires a high level ofskill on the part of the applier to achieve a functional and smoothcast. To facilitate application, it is desirable that the bandagingmaterial be extensible. At least 20% and preferably 25%-35%extensibility is necessary in material of 100 mm width to conform easilyaround the heel of a medium size adult.

Like most knitted fabrics, fiberglass knits tend to curl or fray at acut edge as the yarns are severed and adjacent loops unravel. Frayingand raveling produce unsightly ends and, in the case of an orthopediccast, frayed ends may interfere with the formation of a smooth cast, andloose, frayed ends may be sharp and irritating after the resin thereonhas cured. Accordingly, frayed edges are considered a distinctdisadvantage in orthopedic casting tapes.

Stretchy fiberglass fabrics which resist fraying are disclosed in U.S.Pat. No. 4,609,578 (Reed), the disclosure of which is incorporated byreference. Thus, it is well known that fraying of fiberglass knits atcut edges can be reduced by passing the fabric through a heat cyclewhich sets the yarns giving them new three-dimensional configurationsbased on their positions in the knit. Fiberglass fabrics intended to becoated or impregnated with a resin are sometimes put through aheat-setting process for the additional purpose of removing sizing fromglass filaments which may otherwise interfere with the properapplication of the resin.

A batch process recommended by Owens-Corning Fiberglass Corporation,Toledo, Ohio to remove the sizing on the glass filaments results in aheat-set fabric and consists of the following steps:

1. Start at 100° C. for 1.5 hours;

2. Raise to 250° C. over a period of 5 hours and hold for 12 hours;

3. Raise to 370° C. over a period of 3 hours and hold for 33 hours;

4. Cool to room temperature.

A continuous process involving much less time is also possible.

When a fiberglass fabric which has been heat-set is cut, there isminimal fraying and when a segment of yarn is removed from the heat-setfabric and allowed to relax, it curls into the crimped shape in which itwas held in the knit. Accordingly, at the site of a cut, the severedyarns have a tendency to remain in their looped or knotted configurationrather than to spring loose and cause fraying.

In processing extensible fiberglass fabrics according to U.S. Pat. No.4,609,578 (Reed), a length of fabric is heat-set with essentially notension. The fabric is often wound onto a cylindrical core so largebatches can be processed at one time in a single oven. Care must betaken to avoid applying undue tension to the fabric during wind-up onthe knitter which would distort the knots and loops. To prevent applyingtension to the fabric during winding, the winding operation ispreferably performed with a sag in the fabric as it is wound on thecore.

Prior to the present invention, rolls of moving webs of fabric weretypically either (1) wound with some degree of tension (therebydistorting the knots and loops) or (2) wound loosely in the form of awide web (e.g., >50 mm width) so that the roll would not telescope andthe web could be steered and uniformly processed. Unfortunately, narrowwebs (i.e., webs having a width less than about 50 mm) easily telescopeor collapse when wound loosely on the core and also easily "neck-down"(i.e., the narrow web distorts forming a narrower than desired width) inresponse to even minimal knitting or winding forces which aretransmitted to the free edges of the tape. Wide webs are alsosusceptible to neck-down. These problems have made it difficult to andgreatly increased the cost of producing narrow webs with goodextensibility and webs of uniform width.

SUMMARY OF THE INVENTION

The present invention provides a narrow orthopedic casting tape whichhas a high degree of extensibility and can be handled in longer lengthssuitable for economical production of coated fabric products. The narrowcasting tape of the present invention is knitted as a wide fiberglassfabric with at least one removable connecting yarn in the length (i.e.,warp) direction of the fabric which acts to connect two narrower stripsof fiberglass fabric. The wider fabric is first formed and wound arounda core, then removable connecting yarn is subsequently removed from thefabric by a heat treatment process which separates the wider fabric intotwo narrower fabrics and also heat sets the fabric. Alternatively, theremovable connecting yarn may be removed from the fabric by adissolution process. By either method of removal, removal of one (ormore) such removable connecting yarn(s) causes the wider fabric toseparate into two (or more) narrower fabrics.

The presence of the removable connecting yarns between the strips of theknitted fiberglass fabric allows the fabric to be handled normally,i.e., allowing nearly tension free winding, until the fabric is heatset. The presence of the removable connecting yarn in the knittedfiberglass fabric also resists neck-down of the fabric as it comes offthe needle bed and controls the uniformity of the fabric width for wideor narrow fabrics.

Narrow fabrics of the present invention can also be constructed oforganic yarns. Such narrow casting tape of the present invention is alsoknitted as a wide fabric with at least one removable connecting yarn inthe length direction of the fabric which acts to connect two narrowerfabrics. The removable connecting yarn is subsequently removed from theorganic fabric by a dissolution process. The removal of the removableconnecting yarn(s) causes the fabric to separate into narrower webs. Thepresence of the removable connecting yarn in the knitted fabric allowsthe fabric to be handled normally and to resist necking-down therebycontrolling the uniformity of the fabric width.

The present invention also provides a tearable orthopedic casting tapewhich has a high degree of extensibility. The tearable casting tape ofthe present invention is knitted as a wide fabric, preferablyfiberglass, with at least one tearable connecting yarn in the lengthdirection of the fabric which acts to weakly connect two or morenarrower fabrics. The tearable connecting yarn is capable of beingeasily torn or slit causing the fabric to separate into narrower webs.The presence of the tearable connecting fiber in the knitted castingfabric allows the fabric to be handled normally and be wrapped onto thelimb as a wide casting tape. When desired this wide casting tape may beeasily torn into narrower strips and wrapped around small projectionssuch as a thumb or a pin.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a two bar Raschel knit in which bar 1 performs a simple chainstitch and bar 2 performs lapping motions to lay in yarn.

FIG. 2 is a three bar Raschel knit in which bar 1 performs a simplechain stitch and bars 2 and 3 perform lapping motions to lay in yarn.

FIG. 3 is a four bar Raschel knit in which bar 1 performs a simple chainstitch and bars 2, 3 and 4 perform lapping motions to lay in yarn.

FIG. 4 is a depiction of bar 2 of a two, three or four bar Raschel knitin which the yarns comprise either fabric yarns (shown as lightweightlines) or connecting yarns (shown as heavyweight lines).

FIG. 5 is a depiction of a two bar "latch hook" Raschel knitter in whichfour needles are shown knitting four chain stitches and a lay in stitch.For the purposes of this invention, one might alternatively employ a"compound needle" Raschel knitter which is not shown.

FIG. 6 is a depiction of a two bar Raschel knit in which bar 1 performsa simple chain stitch and bar two performs lapping motion to lay inyarn. The bars are depicted in a overlapping view and further depict achain stitch connecting yarn (shown as a heavyweight line).

DETAILED DESCRIPTION OF THE INVENTION

The substrate of the casting tape of the present invention is preferablyknitted with a combination of organic and inorganic yarns. The yarns arefabricated from multiple individual organic fibers or inorganic fibersor both. As used herein "fiber" refers a slender and greatly elongatednatural or synthetic filament capable of being spun or formed into yarn.Casting tape substrates are often characterized as made from inorganic(e.g., glass) fibers or filaments which are formed into yarn, sized andknitted into a desired fabric. Alternatively, casting tapes of thepresent invention may be made exclusively from organic yarns.

In the present invention the substrates are presently preferably knittedon a Raschel Knitting Machine having 2 to 13 needles per centimeter(cm). The cast substrate fabrics of the present invention are knittedfabrics which may include, for example, an inorganic yarn (e.g.,comprising high modulus fiberglass), an organic yarn (e.g., comprisingpolyester fibers), or a combination of the two when the fabric isknitted.

Yarns are generally structures with a high degree of fiber orientationwith respect to the principal axis of the material. The degree of fiberparallelism and orientation varies from one type of yarn to another, andcan be controlled by fiber type and processing. Spun yarns are producedfrom fibers by a combination of processing steps referred tocollectively as yarn spinning. After preliminary fiber alignment, thefibers are locked together by twisting the structure to form the spunyarn which is continuous in length and substantially uniform. Yarnsproduced from continuous filament synthetic fibers (e.g., fiberglass)are called multifilament yarns and are characterized by nearly completefilament alignment and parallelism with respect to the yarn axis. Thedegree of twist is usually quite low and just adequate to produce someinterfilament cohesion.

When used as a connecting yarn, the yarn may be comprised of anysuitable combustible, dissolvable or tearable organic fiber or tearableinorganic fiber. Suitable organic fibers include synthetic polymerfibers as well as natural organic fibers. The organic fiber may alsocomprise natural rubber or a synthetic elastomer although these are notpreferred.

Suitable synthetic polymer connecting fibers include; naturally basedorganic polymers such as acetate, azlon, rayon, and triacetate; andsynthetically prepared organic polymers such as acrylic, aramid, nylon,olefin (e.g., poly(1-butene), polyethylene, poly(3-methyl-1-butene),poly(1-pentene), polypropylene, and polystyrene), polyester,polytetrafluoroethylene, poly(vinyl alcohol), poly(vinyl chloride), andpoly(vinylidine chloride). Preferred synthetic polymer fibers include;acetate, acrylic, nylon, polyethylene, polypropylene, polyester, andrayon. Most preferred synthetic polymer fibers include; acetate,acrylic, nylon, polyester, and rayon.

Suitable natural organic connecting fibers include: vegetable derivedmaterials such as abaca, cotton, flax, hemp, jute, kapok, linen, ramie,and sisal; and animal derived materials such as wool, mohair, vicuna,other animal hairs, and silk. Preferred natural organic fibers include:cotton and wool. Cotton is most preferred.

Suitable elastomeric connecting fibers include natural rubber,polyisoprene, polybutadiene, diene styrene copolymers, ethylenepropylene copolymers, ethylene propylene diene terpolymers, styrenebutadiene block copolymers, styrene isoprene block copolymers, andpolyurethanes such as spandex.

Suitable inorganic connecting fibers include glass, metallic, andceramic fibers.

The yarns of the fabric itself may be comprised of any suitablehigh-strength high-modulus fiber or filament. Preferred fabric yarnscomprise polymer fibers (e.g., polyester) as well as inorganic fiberssuch as glass, metal, and ceramic fibers. Glass fibers are presentlymost preferred.

Fiberglass knitted fabrics with good extensibility are achievable withtwo common knitting methods: Raschel and tricot. Raschel knitting isdescribed in "Raschel Lace Production" by B. Wheatley (published by theNational Knitted Outerwear Association, 51 Madison Avenue, New York,N.Y. 10010) and "Warp Knitting Production" by Dr. S. Raz (published byHeidelberger Verlagsanstadt und Druckerei GmbH, Hauptstr. 23, D-6900Heidelberg, Germany). Two, three and four bar Raschel knits can beproduced by regulating the amount of yarn in each stitch. Orthopediccasting tape fabrics are preferably two bar Raschel knits although extrabars may be employed. Factors which affect the extensibility offiberglass Raschel knits are the size of the loops in the "chain"stitch, especially in relation to the diameter(s) of the yarn(s) whichpasses through them, and the amount of a loose yarn in the "layin" or"laid-in" stitch(es). If a chain loop is formed and two strands of layinyarn pass through it which nearly fill the loop, then the loop resistsdeformation and little stretch will be observed. Conversely, if thelayin yarns do not fill the loop, then application of tension willdeform the loop to the limits of the layin yarn diameter and stretchwill be observed.

Typical bar patterns for the knit fabric substrates of the presentinvention are shown in the drawings.

FIG. 1 is a two bar Raschel knit in which bar 1 performs a simple chainstitch and bar 2 performs lapping motions to lay in yarn.

FIG. 2 is a three bar Raschel knit in which bar 1 performs a simplechain stitch and bars 2 and 3 perform lapping motions to lay in yarn.

FIG. 3 is a four bar Raschel knit in which bar 1 performs a simple chainstitch and bars 2, 3 and 4 perform lapping motions to lay in yarn.

FIG. 4 is a depiction of bar 2 of a two, three or four bar Raschel knitin which the yarns comprise either fabric yarns (shown as lightweightlines) or connecting yarns (shown as heavyweight lines).

FIG. 5 is a depiction of a two bar "latch hook" Raschel knitter in whichfour needles are shown knitting four chain stitches and a lay in stitch.For the purposes of this invention, one might alternatively employ a"compound needle" Raschel knitter which is not shown.

FIG. 6 is a depiction of a two bar Raschel knit in which bar 1 performsa simple chain stitch and bar two performs lapping motion to lay inyarn. The bars are depicted in a overlapping view and further depict achain stitch connecting yarn (shown as a heavyweight line). It should beunderstood that the above bar patterns may be modified. For example, thelay in stitches could be made to overlap additional chain stitches.

For orthopedic casting material, the fabric selected (preferablyfiberglass), in addition to having the extensibility requirement notedabove, should be of a suitable thickness and mesh size to insure goodpenetration of the curing agent into the roll of resin-coated tape andto provide a finished cast with adequate strength and porosity. Suchfabric parameters are well-known to those skilled in the art and aredescribed in U.S. Pat. No. 4,502,479 which is herein incorporated byreference.

The present invention provides wide knit fabrics comprising one or moreconnecting yarns which connect two or more narrower fabrics. Preferably,the narrower fabrics are made of inorganic yarns such as fiberglass. Theconnecting yarns may either comprise removable yarns (e.g., yarns whichare capable of removal from the fabric through combustion ordissolution) or tearable yarns (i.e., yarns which have a low tearstrength relative to the yarns of the adjacent connected fabrics and maytherefore be selectively torn from the fabric). Either type ofconnecting yarn is knitted into the fabric in a manner such that thefabric yarns form separate strips connected by the connecting yarns.

When the casting material is a fiberglass fabric, suitable removableconnecting yarns are made of fibers which are combustible attemperatures lower than the degradation temperature of the inorganicfibers (e.g., glass fibers) of the connected fabric. Preferably thecombustion temperature of the removable connecting yarn is less than thetemperature commonly used for heat setting fiberglass yarns. Morepreferably the combustion temperature of the removable connecting yarnis between about 200° C. and 540° C. Most preferably the combustiontemperature of the removable connecting yarn is between about 300° C.and 540° C. Heating the fabric to temperatures above about 540° C.should be avoided as subjecting the fiberglass to temperatures ofgreater than about 540° C. can weaken the fiberglass yarns in the fabricwhich may result in reduced strength of casts made from such fabrics.Preferably the tape is not heated above 480° C.

Furthermore, in order to avoid localized degradation of the fabric, theremovable connecting yarn is also preferably a low denier yarn. It ispresently believed that high denier and/or high heat of combustion yarnsgenerate high localized heating during their combustion. These highlocalized heating should be avoided. Preferably the yarn is less than500 denier. More preferably the yarn is less than 250 denier. Mostpreferably the yarn is less than 100 denier.

Alternatively, the removable connecting yarn may comprise fibers whichare capable of dissolving in a gas or solution which doesn't dissolvethe connected fabrics. A suitable removable yarn may be made ofpoly(vinyl alcohol) fibers which may be dissolved in water. Anothersuitable dissolvable yarn may be made of acetate fibers which may bedissolved in acetone. Acetate yarns are preferred because acetone isreadily removed from the fabric and doesn't interfere with water-curableisocyanate-terminated polyurethane prepolymer coatings. Other dissolvingyarns may also be employed.

Furthermore, it is preferred that the connecting yarn not undergoexcessive shrinkage during the removal process. It is presently believedthat excessive shrinkage prior to removal or during the removal processcould distort the fabric. Preferably the yarn has less than about 25%shrinkage. More preferably the yarn has less than about 10% shrinkage.Most preferably the yarn has less than about 5% shrinkage.

Suitable tearable connecting yarns comprise fibers which have a suitablylow tensile strength such that the tearable connecting yarn easily tearswhen a tensile force is applied. The tearable yarn should have asufficiently low tear strength, relative to the yarns which form theconnected fabrics, such that the tearable yarn tears before the fabricyarns. The tearable connecting yarn should be strong enough to hold theconnected fabric strips together during processing and during normal useprior to the tearing operation. Suitable fabric yarns for use in thisinvention have a tensile strength of at least about 2 kg. Preferably thefabric yarns have a tensile strength of between about 2 and about 3 kg.Preferably the tearable connecting yarns have a tensile strength ofbetween about 5% and 50% of the tensile strength of the fabric yarns.Most preferably the tearable connecting yarns have a tensile strength ofbetween about 10% and 25% of the tensile strength of the fabric yarns.

Alternatively, when the fabric comprises inorganic yarns, a tearableconnecting yarn may comprise both inorganic and organic fibers (e.g., ablend of a small number of inorganic fibers with a larger number oforganic fibers). A blend yarn has the advantage that the organic fibersprovide strength to the yarn during knitting but may be selectivelyburned out during the heat-setting process to facilitate tearing. Uponremoval of the organic portion of the connecting yarn, the inorganicfibers of the blended connecting yarn connect the fabric halves of thetape. This yarn tears more easily than the stronger inorganic yarns dueto its smaller bundle count. Preferably the blended connecting yarnshave a tensile strength, after removal of the organic fibers, of betweenabout 5% and 50% of the tensile strength of the inorganic yarns. Mostpreferably the tearable connecting yarns have a tensile strength, afterremoval of the organic fibers, of between about 10% and 25% of thetensile strength of the inorganic yarns.

In one embodiment, the fabric of the present invention is knit withconnecting yarns and inorganic fabric yarns. When used as a removableconnecting yarn the connecting yarn is preferably organic and isselectively knitted into the fabric at intervals along the width of thefabric such that the fabric comprises two or more separate strips ofinorganic fabric connected by the organic yarn(s). Preferably, fabricsof the present invention (when in the connected form) are wider thanabout 50 mm prior to removal of the organic connecting yarn(s). Morepreferably, fabrics of the present invention (when in the connectedform) are wider than about 100 mm prior to removal of the organicconnecting yarn(s). Very wide fabric rolls (when in the connected form)might inhibit the air flow and/or heat transfer in a convection oven.Care should be taken to ensure proper ventilation and heat capacity whenheat desizing very wide connected rolls. Preferably, after removal ofthe organic connecting yarn(s), the narrow fabric is less than 50 mmwide. More preferably, after removal of the organic connecting yarn(s),the narrow fabric is less than 30 mm wide.

The removable connecting yarn(s) may be knit into the fabric either as alaid-in stitch or as a chain stitch. Preferably, the removableconnecting yarn(s) is knit into the fabric as a laid-in stitch. Theessential requirements of a connecting yarn are that it be capable ofknitting with the fabric yarn and connect two fabrics. Therefore, whenthe connecting yarn is removed, e.g., through combustion or dissolution,the fabric remains present in the form of two or more narrower fabricstrips.

When the removable connecting yarn is present as laid-in yarns it ispreferably present as two or more parallel laid-in yarns. While onelaid-in yarn is perfectly acceptable, it has been found that two or moreadjacent and parallel removable laid-in yarns provides better control ofthe fabric prior to removal. Most preferably, three parallel laid-inyarns form the connecting yarn.

The removable connecting yarn may also be a chain stitch yarn. When theremovable connecting yarn is knitted in the form of a chain stitch it isnecessary that the fabric laid-in yarns not bridge the connecting yarnand connect the two adjacent fabric chain stitch yarns. Were thisconstruction formed, the fabric would not separate into two narrowerfabrics upon the removal of the removable connecting yarn. When theremovable connecting yarn is knitted in the form of a chain stitch theresulting fabric has extended loops on the edge of the fabric where thechain stitch has been removed.

When used as a tearable connecting yarn the tearable connecting yarn ispreferably organic and is selectively knitted into the fabric atintervals along the width of the fabric such that the fabric comprisestwo or more separate strips of inorganic fabric connected by thetearable organic yarn(s). Preferably, fabrics of the present inventionhave tearable connecting yarns at less than about 50 mm intervals. Morepreferably, fabrics of the present invention have tearable connectingyarns at about 25 mm intervals. The exact position of the tearableconnecting yarns may be adjusted depending on the width of the fabric orthe intended application of the casting tape. To facilitate tearing itmay be desirable to color (e.g., pigment or dye) the tearable yarn acontrasting color from the higher strength fabric yarns. This will allowthe user more easily to focus stress at the tearable yarn during thetearing step.

The tearable connecting yarn may be knit into the fabric either as alaid-in stitch or as a chain stitch. Preferably, the tearable connectingyarn is knitted into the fabric as a laid-in stitch. The essentialrequirements of a connecting yarn are that it be capable of knittingwith the fabric yarn and connect two fabrics. Therefore, when theconnecting yarn is torn the fabric remains present in the form of two ormore narrower fabric strips.

When the tearable connecting yarn is present as laid-in yarns it ispreferably present as one yarn. Two or more parallel yarns may also beutilized but are not preferred.

The tearable yarn may also be present as a chain stitch yarn althoughthis is not preferred. When the tearable connecting yarn is knitted inthe form of a chain stitch it is necessary that the fabric laid-in yarnsnot bridge the connecting yarn and connect the two adjacent fabric chainstitch yarns. Were this construction formed, the fabric would not teareasily into two narrower fabrics.

In processing the knitted fiberglass fabric of the present invention, alength of fabric is optionally, and preferably, heat-set withessentially no tension. Preferably, the fabric is wound onto acylindrical core so large batches can be processed at one time in asingle oven. Care must be taken to avoid applying undue tension to thefabric which would distort the knots and loops. A continuousheat-setting process may also be used in which a length of fabric isplaced without undue tension on a moving conveyor system and passedthrough an oven for sufficient time and temperature to achieve heatsetting of the fabric.

The heat-setting step may be performed in a number of conventional waysknown to the art. In heat-setting a small piece of fabric, e.g., 25centimeters of tape, in a single layer, a temperature of 425° C. forthree minutes has been found to be sufficient. To achieve optimumsetting, a temperature of 540° .C for three minutes is required.Equivalent setting at lower temperatures is possible, but longer time isrequired. Batch processes require a longer residence time at theselected temperature due to the mass of glass fabric which must beheated.

The optimum heat-setting process described above is sufficient in mostcases to remove the sizing from the fabric. However, the process of thepresent invention may also be practiced using partially heat-desized ora chemically-desized fabric. Chemical desizing processes are describedin U.S. Pat. Nos. 3,686,725; 3,787,272; and 3,793,686. Heat desizingprocesses are described in U.S. Pat. No. 4,609,578.

The fabric is preferably cooled prior to application of the resin. Theresin selected to apply to the heat-set fabric is dictated by theend-use of the product. For orthopedic casting materials, suitableresins are well-known and described for example, in U.S. Pat. Nos.4,376,438; 4,433,680; 4,502,479; and 4,667,661 which are hereinincorporated by reference. The preferred resins are the moisture-curableisocyanate-terminated polyurethane prepolymers described in theaforementioned patents. The amount of such resin applied to thefiberglass tape to form an orthopedic casting material is typically anamount sufficient to constitute 35 to 50 percent by weight of the final"coated" tape. The term "coated" or "coating" as used herein withrespect to the resin refers generically to all conventional processesfor applying resins to fabrics and is not intended to be limiting. Inthe case of tearable yarns, it is desirable that the tearable yarns notswell or dissolve in the resin.

To insure storage stability of the coated tape, it must be properlypackaged, as is well known in the art. In the case of water-curableisocyanate-terminated polyurethane prepolymer resin systems, moisturemust be excluded. This is typically accomplished by sealing the tape ina foil or other moisture-proof pouch.

In addition to the application of the present invention to the field oforthopedic casting tapes, other uses may include wrapping and/or joiningpipes, cables or the like; patching or bridging gaps to provide asurface for filling and repairs; etc.

The invention may be further illustrated by the following workingexamples which are merely illustrative and not intended to be limitingin any way.

EXAMPLE 1 Preparation of a Narrow Casting Tape

Fiberglass tape was knit on a two bar Raschel warp knitter usingfiberglass yarn (ECDE 75 1/0.7Z Sizing PPG610; available from PPGIndustries Inc.) and polyester connecting yarn (1/70/34 T-56 dyedpolyester yarn; available from UNIFI, Inc.). The fabric was a two bar,18 gauge construction consisting of an open chain stitch and a layinstitch which overlaps 4 needles. The fabric characteristics are: 0.5wales per mm; 0.6 courses per mm; chain stitch runner length of 3.73meters (m); layin stitch runner length of 3.7 meters. A relaxed sectionof tape 254 mm in length can be extended to a length of 337 mm whenmanually held taut (32.5% stretch).

The tape was 71 mm wide as knit. Three polyester yarns were knit aslayin stitch yarns, in place of fiberglass yarns, at the midpoint of thetape. The polyester connecting yarns were tensioned at 5 gm. This amountof tension was sufficient to hold the two narrower webs together yet notan excessive amount which would deform the webs. The tape was then woundon a metal core into a roll which contains about 412 meters of tape. Thewinding operation was performed with a sag in the tape as it was rolledonto the core. Therefore, there was essentially no tension applied tothe tape. The loose roll of fiberglass tape (with polyester connectingyarns) was then placed in a cool oven. The oven was closed and set toreach 421° C. within 1 hour. After 8 hours the heat was turned off andthe oven, while remaining closed, was allowed to cool to 360° C. Theoven was then opened and further allowed to cool to 240° C. The tape wasthen removed from the oven in the form of two separate narrower rollswith a gap where the now combusted polyester yarns had been. The rollswere separately placed on a motorized spindle, and the tape was fed overa roller and 3.6 meters of tape was rewound on a core. At the rollerstation a liquid isocyanate-terminated polyurethane prepopolymer resinwas extruded onto the tape so that the coated tape has 42.5% by weightresin. The unwind and windup tensions were adjusted to a minimum but nosag was present. The rolling operation was also under minimum tension sothe coated tape was not stretched as it was taken up by the core. Theroll of tape was then packaged in a plastic/aluminum laminate pouchimpervious to water which was then heat-sealed. Tape removed from thepouch exhibits 30% extensibility in the lengthwise direction.

EXAMPLE 2 Preparation of a Narrow Organic Casting Tape

Polyester tape is knit on a two bar Raschel warp knitter using polyesterfabric yarn and acetate connecting yarn. The fabric is a two bar, 18gauge construction consisting of an open chain stitch and a layin stitchwhich overlaps 4 needles. The fabric characteristics are: 0.5 wales permm; 0.6 courses per mm; chain stitch runner length of 3.73 meters (m);layin stitch runner length of 3.7 meters.

The tape is 71 mm wide as knit. Three acetate yarns are knit as layinstitch yarns, in place of polyester yarns, at the midpoint of the tape.The acetate connecting yarns are tensioned at 5 gm. This amount oftension is sufficient to hold the two narrower webs together yet not anexcessive amount which would deform the webs. After knitting, the tapeis passed through an acetone solvent bath to dissolve the acetateconnecting yarns and thereby separate the fabric into two narrowerfabrics. The acetone is then recovered from the tape by an evaporationprocess and a liquid isocyanate-terminated polyurethane prepopolymerresin is extruded onto the tape to form a narrow casting tape. The rollof tape is then packaged in a plastic/aluminum laminate pouch imperviousto water which is then heat-sealed.

EXAMPLE 3 Preparation of a Narrow Inorganic Casting Tape

Fiberglass tape is knit on a two bar Raschel warp knitter usingfiberglass fabric yarn and polyvinyl alcohol ("PVA") connecting yarn.The fabric is a two bar, 18 gauge construction consisting of an openchain stitch and a layin stitch which overlaps 4 needles. The fabriccharacteristics are: 0.5 wales per mm; 0.6 courses per mm; chain stitchrunner length of 3.73 meters (m); layin stitch runner length of 3.7meters.

The tape is 71 mm wide as knit. Three PVA yarns are knit as layin stitchyarns, in place of fiberglass yarns, at the midpoint of the tape. ThePVA connecting yarns are tensioned at 5 gm. This amount of tension issufficient to hold the two narrower webs together yet not an excessiveamount which would deform the webs. After knitting, the tape is passedthrough an aqueous solvent bath to: (1) dissolve the PVA connectingyarns; (2) desize the fiberglass yarns; and (3) thereby separate thefabric into two narrower fabrics. The solvent is then recovered from thetape by an evaporation and drying process and a liquidisocyanate-terminated polyurethane prepopolymer resin is extruded ontothe tape to form a narrow casting tape. The roll of tape is thenpackaged in a plastic/aluminum laminate pouch impervious to water whichis then heat-sealed.

EXAMPLE 4 Preparation of a Tearable Organic Casting Tape

Polyester tape is knit on a two bar Raschel warp knitter using polyesterfabric yarn and cotton connecting yarn. The fabric is a two bar, 18gauge construction consisting of an open chain stitch and a layin stitchwhich overlaps 4 needles. The fabric characteristics are: 0.5 wales permm; 0.6 courses per mm; chain stitch runner length of 3.73 meters (m);layin stitch runner length of 3.7 meters.

The tape is 71 mm wide as knit. Three cotton yarns are knit as layinstitch yarns, in place of polyester yarns, at the midpoint of the tape.The cotton connecting yarns are tensioned at 5 gm. This amount oftension is sufficient to hold the two narrower webs together yet not anexcessive amount which would deform the webs or tear the cotton yarn.After knitting, the tape is coated with an isocyanate-terminatedpolyurethane prepopolymer resin to form a casting tape. The roll of tapeis then packaged in a plastic/aluminum laminate pouch impervious towater which is then heat-sealed. Tape removed from the pouch exhibitsgood extensibility in the lengthwise direction and may be easily tornlengthwise to form two narrower fabric strips.

EXAMPLE 5 Preparation of a Tearable Inorganic Casting Tape

Fiberglass tape is knit on a two bar Raschel warp knitter usingfiberglass yarn (ECDE 75 1/0.7Z Sizing PPG610; available from PPGIndustries Inc.) and a blend of fiberglass and polyester connecting yarn(comprising 10% glass fibers and 90% polyester fibers). The fabric is atwo bar, 18 gauge construction consisting of an open chain stitch and alayin stitch which overlaps 4 needles. The fabric characteristics are:0.5 wales per mm; 0.6 courses per mm; chain stitch runner length of 3.73meters (m); layin stitch runner length of 3.7 meters. A relaxed sectionof tape 254 mm in length can be extended to a length of 337 mm whenmanually held taut (32.5% stretch).

The tape is 71 mm wide as knit. Three blend yarns are knit as layinstitch yarns, in place of fiberglass yarns, at the midpoint of the tape.The blend connecting yarns are tensioned at 5 gm. This amount of tensionis sufficient to hold the two narrower webs together yet not anexcessive amount which would deform the webs. The tape is then wound ona metal core into a roll which contains about 412 meters of tape. Thewinding operation is performed with a sag in the tape as it was rolledonto the core. Therefore, there is essentially no tension applied to thetape. The loose roll of fiberglass tape (with blend connecting yarns) isthen placed in a cool oven. The oven is closed and set to reach 421° C.within 1 hour. After 8 hours the heat is turned off and the oven, whileremaining closed, is allowed to cool to 360° C. The oven is then openedand further allowed to cool to 240° C. The tape is then removed from theoven in the form of a wide roll with a smaller bundle count inorganicconnecting yarn where the now combusted polyester fibers had been. Theroll is placed on a motorized spindle, and the tape is fed over a rollerand 3.6 meters of tape is rewound on a core. At the roller station aliquid isocyanate-terminated polyurethane prepopolymer resin is extrudedonto the tape so that the coated tape has 42.5% by weight resin. Theunwind and windup tensions are adjusted to a minimum but no sag ispresent. The rolling operation is also under minimum tension so thecoated tape is not stretched as it is taken up by the core. The roll oftape is then packaged in a plastic/aluminum laminate pouch impervious towater which is then heat-sealed. Tape removed from the pouch exhibits30% extensibility in the lengthwise direction and may be easily tornlengthwise to form two narrower fabric strips.

What is claimed is:
 1. A method of making narrow fiberglass fabrics,comprising the steps of:knitting a fiberglass fabric comprising: atleast one removable connecting yarn in the warp direction of the fabric,said removable connecting yarn being dissoluble or combustible; and aplurality of fiberglass fabric yarns; winding said connected knit fabricinto a wide roll; and then removing said removable connecting yarn fromsaid wide roll to thereby separate said roll into two or more rolls ofnarrower fiberglass fabric, wherein at least one of said narrowfiberglass fabrics is less than about 50 mm wide after removing saidremovable connecting yarn.
 2. A method according to claim 1, wherein:said removable connecting yarn is combustible; said fiberglass fabricyarn resists combustion; and wherein said removing step comprisesheat-setting said fabric at a temperature sufficient to combustiblyremove said removable connecting yarn.
 3. A method according to claim 2,wherein: said removable connecting yarn comprises fibers selected fromthe group consisting of synthetic polymer fibers and natural organicfibers.
 4. A method according to claim 2, wherein said removableconnecting yarn comprises fibers selected from the group consisting ofacetate azlon, rayon, triacetate, acrylic, aramid, nylon,poly(1-butene), polyethylene, poly(3-methyl-1-butene), poly(1-pentene),polypropylene, polystyrene, polyester, polytetrafluoroethylene,poly(vinyl alcohol), poly(vinyl chloride), poly(vinylidine chloride),abaca, cotton, flax, hemp, jute, kapok, linen, ramie, sisal, wool,mohair, vicuna, and silk.
 5. A method according to claim 2, wherein saidremovable connecting yarn comprises fibers selected from the groupconsisting of polyethylene, polypropylene, polyester, and rayon.
 6. Amethod according to claim 1, wherein said removable connecting yarn isknit into said fabric as one or more laid-in stitches, said laidinstitches connecting two or more fabrics.
 7. A method according to claim5, wherein said removable connecting yarn is knit into said fabric astwo or more adjacent laid-in stitches, said laid-in stitches connectingtwo or more fabrics.
 8. A method according to claim 2, furthercomprising the step of:coating said narrow inorganic fabric with amoisture-curable isocyanate-terminated polyurethane prepolymer.
 9. Amethod according to claim 1, wherein:said wide fabric is at least 50 mmwide prior to removal of said removable connecting yarn; and at leastone of said narrow inorganic fabrics is less than about 30 mm wide afterremoving said removable connecting yarn.
 10. A method according to claim2, wherein:said wide fabric is at least 100 mm wide prior to removal ofsaid removable connecting yarn; and at least one of said narrowinorganic fabrics is less than about 50 mm wide after removing saidremovable connecting yarn.